The higher-rank Godbersen conjecture for Cartesian powers

Let KRnK\subset\mathbb{R}^n be a convex body. Let Δp:Rn(Rn)p\Delta_p:\mathbb{R}^n\to(\mathbb{R}^n)^p be the diagonal embedding, and let ιi:Rn(Rn)p\iota_i:\mathbb{R}^n\to(\mathbb{R}^n)^p be inclusion into the ii-th factor. For a body AA, write A[r]A[r] for rr copies of AA, and let VV denote mixed volume in (Rn)p(\mathbb{R}^n)^p. Higher-rank Godbersen conjecture. For any pNp\in\mathbb{N}, 0kn0\leq k\leq n, and 0kin0\leq k_i\leq n for i=1,,pi=1,\dots,p, such that k1++kp=kk_1+\cdots+k_p=k, one has

V(ΔpK[k],ι1K[nk1],,ιpK[nkp])(nk)(kk1,,kp)(n!)p(pn)!voln(K)p.V(-\Delta_pK[k],\iota_1K[n-k_1],\dots,\iota_pK[n-k_p])\leq {n\choose k}{k\choose k_1,\dots,k_p}\frac{(n!)^p}{(pn)!}\operatorname{vol}_n(K)^p.

Moreover, if ki<nk_i<n for all ii, 0<k0<k, and KK has nonempty interior, equality holds if and only if KK is a simplex. This conjecture strengthens the higher-order Godbersen conjecture; the paper proves both for anti-blocking convex bodies, but the general assertion remains open.

Sources & referencesView supporting material

Primary source

Jan Kotrbatý, “On a generalization of Godbersen's conjecture”, arXiv:2502.02149 (2025).

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